/* XMLEntityResolver.java                                          NanoXML/Java
 *
 * $Revision: 1.4 $
 * $Date: 2002/01/04 21:03:29 $
 * $Name: RELEASE_2_2_1 $
 *
 * This file is part of NanoXML 2 for Java.
 * Copyright (C) 2000-2002 Marc De Scheemaecker, All Rights Reserved.
 *
 * This software is provided 'as-is', without any express or implied warranty.
 * In no event will the authors be held liable for any damages arising from the
 * use of this software.
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 *  1. The origin of this software must not be misrepresented; you must not
 *     claim that you wrote the original software. If you use this software in
 *     a product, an acknowledgment in the product documentation would be
 *     appreciated but is not required.
 *
 *  2. Altered source versions must be plainly marked as such, and must not be
 *     misrepresented as being the original software.
 *
 *  3. This notice may not be removed or altered from any source distribution.
 */

package net.n3.nanoxml;

import java.io.Reader;
import java.io.StringReader;
import java.util.Hashtable;

/**
 * An XMLEntityResolver resolves entities.
 * 
 * @author Marc De Scheemaecker
 * @version $Name: RELEASE_2_2_1 $, $Revision: 1.4 $
 */
@SuppressWarnings("unchecked")
public class XMLEntityResolver implements IXMLEntityResolver {

	/**
	 * The entities.
	 */
	private Hashtable entities;

	/**
	 * Initializes the resolver.
	 */
	public XMLEntityResolver() {
		this.entities = new Hashtable();
		this.entities.put("amp", "&#38;");
		this.entities.put("quot", "&#34;");
		this.entities.put("apos", "&#39;");
		this.entities.put("lt", "&#60;");
		this.entities.put("gt", "&#62;");
	}

	/**
	 * Cleans up the object when it's destroyed.
	 */
	protected void finalize() throws Throwable {
		this.entities.clear();
		this.entities = null;
		super.finalize();
	}

	/**
	 * Adds an internal entity.
	 * 
	 * @param name
	 *            the name of the entity.
	 * @param value
	 *            the value of the entity.
	 */
	public void addInternalEntity(String name, String value) {
		if (!this.entities.containsKey(name)) {
			this.entities.put(name, value);
		}
	}

	/**
	 * Adds an external entity.
	 * 
	 * @param name
	 *            the name of the entity.
	 * @param publicID
	 *            the public ID of the entity, which may be null.
	 * @param systemID
	 *            the system ID of the entity.
	 */
	public void addExternalEntity(String name, String publicID, String systemID) {
		if (!this.entities.containsKey(name)) {
			this.entities.put(name, new String[] { publicID, systemID });
		}
	}

	/**
	 * Returns a Java reader containing the value of an entity.
	 * 
	 * @param xmlReader
	 *            the current XML reader
	 * @param name
	 *            the name of the entity.
	 * 
	 * @return the reader, or null if the entity could not be resolved.
	 */
	public Reader getEntity(IXMLReader xmlReader, String name) throws XMLParseException {
		Object obj = this.entities.get(name);

		if (obj == null) {
			return null;
		} else if (obj instanceof java.lang.String) {
			return new StringReader((String) obj);
		} else {
			String[] id = (String[]) obj;
			return this.openExternalEntity(xmlReader, id[0], id[1]);
		}
	}

	/**
	 * Returns true if an entity is external.
	 * 
	 * @param name
	 *            the name of the entity.
	 */
	public boolean isExternalEntity(String name) {
		Object obj = this.entities.get(name);
		return !(obj instanceof java.lang.String);
	}

	/**
	 * Opens an external entity.
	 * 
	 * @param xmlReader
	 *            the current XML reader
	 * @param publicID
	 *            the public ID, which may be null
	 * @param systemID
	 *            the system ID
	 * 
	 * @return the reader, or null if the reader could not be created/opened
	 */
	protected Reader openExternalEntity(IXMLReader xmlReader, String publicID, String systemID) throws XMLParseException {
		String parentSystemID = xmlReader.getSystemID();

		try {
			return xmlReader.openStream(publicID, systemID);
		} catch (Exception e) {
			throw new XMLParseException(parentSystemID, xmlReader.getLineNr(), "Could not open external entity " + "at system ID: "
					+ systemID);
		}
	}

}
